Film-to-glass switchable glazing

ABSTRACT

A privacy glazing structure may include an electrically controllable optically active material, such as a liquid crystal material, sandwiched between a flexible substrate and a rigid substrate. The flexible substrate and the rigid substrate may each have a conductive layer deposited on the surface facing the optically active material. The flexible substrate may be bonded about its perimeter to the rigid substrate and may be sufficiently flexible to conform to non-planarity of the rigid substrate. As a result, the flexible substrate may adopt the surface contour of the rigid substrate to maintain a uniform thickness of optically active material between the flexible substrate and the rigid substrate.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/892,251, filed Feb. 8, 2018, which claims priority to U.S.Provisional Patent Application No. 62/456,286, filed Feb. 8, 2017. Theentire contents of each of these applications are incorporated herein byreference.

TECHNICAL FIELD

This disclosure relates to optical structures and, more particularly, toglazing structures that include a controllable optically activematerial.

BACKGROUND

Windows, doors, partitions, and other structures having controllablelight modulation have been gaining popularity in the marketplace. Thesestructures are commonly referred to as “smart” structures or “privacy”structures for their ability to transform from a transparent state inwhich a user can see through the structure to a private state in whichviewing is inhibited through the structure. For example, smart windowsare being used in high-end automobiles and homes and smart partitionsare being used as walls in office spaces to provide controlled privacyand visual darkening.

A variety of different technologies can be used to provide controlledoptical transmission for a smart structure. For example, electrochromictechnologies, photochromic technologies, thermochromic technologies,suspended particle technologies, and liquid crystal technologies are allbeing used in different smart structure applications to providecontrollable privacy. The technologies generally use an energy source,such as electricity, to transform from a transparent state to a privacystate or vice versa.

While privacy technology is gaining popularity, there are stillpractical challenges to successful implementation of the technology. Forexample, if the material used to impart controllable privacy is notuniformly applied across the privacy structure, pockets or regions mayform that are comparatively darker or comparatively lighter than theremainder of the structure when transitioned into the privacy state.This can create an undesirable visual appearance and inconsistentprivacy shielding across the structure. As another example, if thehardware components needed to transform a standard window or doorstructure into a privacy glazing structure are too heavy, a manufacturerof window and door products may not be able to readily utilize suchprivacy glazing structures on existing product lines. Rather, specialproduct designs may be required to accommodate the size and weight ofthe privacy structure, which may be more difficult to implement and findless market acceptance than more standard designs.

SUMMARY

In general, this disclosure is directed to privacy cells and privacyglazing structures incorporating optically active material that providescontrollable privacy. In some examples, a privacy glazing structureincludes multiple rigid substrates and a spacer that holds the rigidsubstrates in parallel alignment and defines a between pane space. Theprivacy glazing structure can further include a flexible substrate thatis bonded about its perimeter to a surface of one of the rigidsubstrates facing the between pane space. A cavity may be definedbetween the flexible substrate and the surface of the rigid substrate towhich the flexible substrate is bonded. An electrically controllableoptically active material may be positioned inside of the cavity toprovide controllable privacy for the glazing structure. The flexiblesubstrate may be sufficiently flexible to conform to any non-planarityof the rigid substrate to which the flexible substrate is bonded.Accordingly, the flexible substrate may conform to surface variations ofthe rigid substrate.

Without wishing to be bound by any particular theory, it has beenobserved that certain rigid substrates used to form a privacy glazingstructure, such as glass sheets, may not be perfectly planar acrosstheir face. Rather, such rigid substrates may exhibit regions that arehigher or lower than adjacent regions across the face of the substrate,such as peaks and valleys that form a waviness across the face of thesubstrate. For example, when using thermally strengthened glass, thethermally strengthened glass may exhibit non-planer distortions impartedduring the strengthening process that can be caused from non-uniformheat transfer and/or unbalanced support of the glass structure. Thesedeformations may be characterized by a resulting defect appearance andmay be described as roller wave or edge kink non-planarity defects. Whenforming a privacy glazing structure using two glass substrates that bothexhibit deformations, such as roller wave and/or edge kink deformations,the thickness of the space between the two glass substrates holding theoptically active material may not be uniform across the face of thestructure. The peaks and valleys of the opposed glass sheets may not bealigned to provide a generally uniform thickness of optically activematerial but may instead be misaligned, creating regions where a peak ofone sheet faces a peak of the opposite sheet, regions where a valley ofone sheet faces a valley of the opposite sheet, and yet further regionswhere a peak of one sheet faces the valley of the opposite sheet.

When a privacy glazing structure has inconsistent spacing between thesurfaces of the substrates holding the optically active material, theoptically active material may be thicker in some regions and thinner inother regions. Indeed, in some situations, the inconsistent spacing maycause voids or pockets to form between the sheets that are devoid ofoptically active material. In either case, when the optically activematerial is transitioned to a darkened or privacy state, theinconsistencies in the thickness of the optically active material maycause some regions of the glazing structure to appear darker than otherregions. For example, the privacy glazing structure may appear darker inareas where the optically active material is thicker than adjacent areaswhere the optically active material is thinner or, in more significantcircumstances, entirely missing. This can cause inconsistencies in thevisual appearance of the privacy glazing structure, such as the level ofprivacy provided across the structure.

By configuring a privacy glazing structure with the flexible substratebonded to a comparatively rigid substrate to form the cavity holding theoptically active material, the flexible substrate may adapt to conformto variations in the surface thickness of the opposed rigid substrate.For example, the flexible substrate may substantially mirror the surfacevariations of the rigid substrate, such that the flexible substratedefines a peak where there is a valley in the opposed rigid substrateand the flexible substrate defines a valley where there is a peak in theopposed rigid substrate. As a result, the thickness of the cavityholding the optically active material may be substantially uniformacross the entirety of the privacy glazing structure even though therigid substrate has surface variations that would otherwise causethickness variations in the cavity. This can provide a more uniformvisual appearance and more uniform privacy across the glazing structurethan if the glazing structure is formed of two rigid substrates thatboth exhibit surface waviness and non-planarity.

In one example, a privacy glazing structure includes a tempered glasssubstrate and a flexible polymeric sheet bonded to the tempered glasssubstrate about its perimeter to define a cavity containing a liquidcrystal material. The tempered glass substrate may exhibit surfacewaviness caused by thermal treatment during the tempering process.However, the tempered glass substrate may be beneficial to impartadditional strength and safety characteristics to the privacy glazingstructure that would not otherwise be achieved if using a standard,non-strengthened glass substrate. The flexible polymeric sheet may besufficiently flexible to conform to the waviness of the tempered glasssubstrate such that the cavity retaining liquid crystal material issubstantially uniform in thickness across the face of the privacyglazing structure. The tempered glass substrate may, in turn, be bondedabout its perimeter to another glass substrate with a spacer to define abetween-pane space between the two glass substrates, which may be filledwith an insulative gas. The flexible polymeric sheet may be positionedinside of the between pane space. As a result, the flexible polymericsheet may be protected from scratches and puncturing by the glass sheetto which the flexible polymeric sheet is bonded.

Configuring a privacy glazing structure with a comparatively flexiblesubstrate bonded to a comparatively rigid substrate with an opticallyactive material retained between the two substrates can be useful forother reasons in addition to or in lieu of providing a substantiallyuniform optically active layer. As one example, a privacy glazingstructure may be made thinner and may weigh less than a comparativeprivacy glazing structure in which all the substrates are formed of amore rigid material, such as glass. This can be useful for incorporatingthe privacy glazing structure into existing product designs that havesize and/or weight restrictions corresponding to the size and/or weightof a standard insulating glass unit that does not have controllableprivacy capabilities. As another example, the flexible substrate may beused to impart UV blocking capabilities for the optically activematerial in addition to forming a wall surface bounding the opticallyactive material. In the case of a liquid crystal optically activematerial, for example, the liquid crystal material may have a tendencyto degrade over time with exposure to UV light from the sun. To helpprotect the liquid crystal material from such UV light, the flexiblesubstrate can carry UV blocking agents and can be positioned on anoutboard side of the privacy glazing structure. Once installed, sunlightentering the privacy glazing structure may pass through the flexiblesubstrate before impinging upon the liquid crystal material and passingtherethrough. Accordingly, the UV blocking properties of the flexiblesubstrate can help filter UV light from the sunshine before it reachesthe liquid crystal material, helping to prevent degradation of theliquid crystal material during the service life of the privacy glazingstructure.

In one example, a privacy glazing structure is described that includes afirst rigid substrate of transparent material and a second rigidsubstrate of transparent material that is generally parallel to thefirst rigid substrate. The second rigid substrate has a first surfaceand a second surface opposite the first surface. The structure furtherincludes a spacer positioned between the first rigid substrate and thesecond rigid substrate to define a between-pane space and a flexiblesubstrate having a first surface and a second surface opposite the firstsurface. The example structure also includes a first substantiallytransparent conductive layer carried on the first surface of theflexible substrate, a second substantially transparent conductive layercarried on the first surface of the second rigid substrate facing thebetween-pane space, and an electrically controllable optically activematerial. The example specifies that the flexible substrate is bondedabout its perimeter to the first surface of the second rigid substrateto form a cavity therebetween, the electrically controllable opticallyactive material is disposed within the cavity, and the flexiblesubstrate is sufficiently flexible to conform to non-planarity of thesecond rigid substrate.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of an example privacy glazing structure accordingto the disclosure.

FIG. 2 is a sectional illustration of the example privacy glazingstructure of FIG. 1 taken along the A-A sectional line illustrated onFIG. 1.

FIG. 3 is a sectional illustration of the example privacy glazingstructure of FIG. 1 taken along the B-B sectional line illustrated onFIG. 1.

FIG. 4 is a side view illustration of the example privacy glazingstructure of FIG. 1 showing an example arrangement of components.

DETAILED DESCRIPTION

In general, this disclosure relates to privacy structures that contain acontrollable optically active material positioned between acomparatively rigid substrate and a comparatively flexible substrate.The term privacy structure includes privacy cells, privacy glazingstructures, smart cells, smart glazing structure, and related devicesthat provide controllable optical activity and, hence, visibilitythrough the structure. Such structures can provide switchable opticalactivity that provides controllable darkening, controllable lightscattering, or both controllable darkening and controllable lightscattering. Controllable darkening refers to the ability of theoptically active material to transition between a high visible lighttransmission state (a bright state), a low visible light transmissiondark state, and optionally intermediate states therebetween, and viceversa, by controlling an external energy source applied to the opticallyactive material. Controllable light scattering refers to the ability ofthe optically active material to transition between a low visible hazestate, a high visible haze state, and optionally intermediate statestherebetween, and vice versa, by controlling an external energy source.Thus, reference to the terms “privacy” and “privacy state” in thepresent disclosure does not necessarily require complete visibleobscuring through the structure (unless otherwise noted). Rather,different degrees of privacy or obscuring through the structure may beachieved depending, e.g., on the type of optically active material usedand the conditions of the external energy source applied to theoptically active material.

In some examples, a privacy structure is in the form of a multiple-paneinsulating glazing unit having first and second panes of transparentmaterial along with a spacer separating the transparent panes ofmaterial to provide a between-pane space. The multiple-pane insulatingglazing unit carries a layer of electrically controllable opticallyactive material positioned behind one of the panes of transparentmaterial within the between-pane space. The electronically controllableoptically active material can be controllably alternated between a lighttransmissive state and a privacy state, such as a light scatteringand/or light absorbing state. When placed in the privacy state, lightimpinging upon the optically active material can scatter and/or absorbrather than pass through the material, obscuring visibility through thematerial to an external observer. The electronically controllableoptically active material may be retained in the between-pane space bysandwiching the material against the interior surface of one of thepanes of transparent material with a flexible substrate. The flexiblesubstrate can flex and bend to conform to variations in the surfacewaviness of the opposite pane of transparent material against which theoptically active material is sandwiched.

Although the configuration and positioning of the flexible substrate canvary, in some examples, the flexible substrate is selected to becompatible with and/or provide synergistic properties for the othercomponents of the privacy glazing structure. For instance, in someexamples, the flexible substrate is selected to have a coefficient ofthermal expansion substantially consistent with the coefficient ofthermal expansion of the opposed substrate to which the flexiblesubstrate is bonded. This may help prevent the flexible substrate frompulling away or otherwise detaching from the substrate to which it isbonded during thermal cycling. As another example, the flexiblesubstrate may be selected to provide UV blocking capabilities, therebyhelping to filter light within the ultraviolet wavelengths beforeimpinging upon the optically active material positioned behind theflexible substrate. This can help prevent degradation and prematuredeterioration of the optically active material over the service life ofthe privacy glazing structure. A privacy glazing structure can have avariety of different components and configurations, as described ingreater detail herein.

FIG. 1 is a side view of an example privacy glazing structure 12 thatincludes a first substrate of transparent material 14 spaced apart fromthe second substrate of transparent material 16 by a spacer 18 to definea between-pane space 20. Spacer 18 may extend around the entireperimeter of privacy glazing structure 12 to hermetically seal thebetween-pane space 20 from gas exchange with a surrounding environment.In the illustrated example, privacy glazing structure also includes alayer of optically active material 22 positioned on a side of secondsubstrate 16 facing the between-pane space 20. In addition, thestructure includes a layer formed of comparatively flexible material 24sandwiching the layer of optically active material 22 against the secondsubstrate 16. The layer of optically active material 22 can transitionfrom a generally transparent state to a privacy state to controlvisibility through privacy glazing structure 12. In the privacy state,the layer of optically active material 22 may be dark and/or hazy,obscuring viewing through the material.

Privacy glazing structure 12 can utilize any suitable privacy materialsfor the layer of optically active material 22. Further, althoughoptically active material 22 is generally illustrated and described asbeing a single layer of material, it should be appreciated that astructure in accordance with the disclosure can have one or more layersof optically active material with the same or varying thicknesses. Ingeneral, optically active material 22 is configured to providecontrollable and reversible optical obscuring and lightening. Opticallyactive material 22 can change visible transmittance in response to anenergy input, such as light, heat, or electricity. For example,optically active material 22 may be an electronically controllableoptically active material that changes direct visible transmittance inresponse to changes in electrical energy applied to the material.

In one example, optically active material 22 is formed of anelectrochromic material that changes opacity and, hence, lighttransmission properties, in response to voltage changes applied to thematerial. Typical examples of electrochromic materials are WO₃ and MoO₃,which are usually colorless when applied to a substrate in thin layers.An electrochromic layer may change its optical properties by oxidationor reduction processes. For example, in the case of tungsten oxide,protons can move in the electrochromic layer in response to changingvoltage, reducing the tungsten oxide to blue tungsten bronze. Theintensity of coloration is varied by the magnitude of charge applied tothe layer.

In another example, optically active material 22 is formed of a liquidcrystal material. Different types of liquid crystal materials that canbe used as optically active material 22 include polymer dispersed liquidcrystal (PDLC) materials and polymer stabilized cholesteric texture(PSCT) materials. Polymer dispersed liquid crystals usually involvephase separation of nematic liquid crystal from a homogeneous liquidcrystal containing an amount of polymer, sandwiched between electrodes.The electrodes can be formed by coating opposed substrates (e.g., secondsubstrate 16 and flexible substrate 24) with a transparent conductivematerial. When the electric field is off, the liquid crystals arerandomly scattered. This scatters light entering the liquid crystal anddiffuses the transmitted light through the material. When a certainvoltage is applied between the two electrodes, the liquid crystalshomeotropically align and the liquid crystals increase in opticaltransparency, allowing light to transmit through the crystals.

In the case of polymer stabilized cholesteric texture (PSCT) materials,the material can either be a normal mode polymer stabilized cholesterictexture material or a reverse mode polymer stabilized cholesterictexture material. In a normal polymer stabilized cholesteric texturematerial, light is scattered when there is no electrical field appliedto the material. If an electric field is applied to the liquid crystal,it turns to the homeotropic state, causing the liquid crystals toreorient themselves parallel in the direction of the electric field.This causes the liquid crystals to increase in optical transparency andallows light to transmit through the liquid crystal layer. In a reversemode polymer stabilized cholesteric texture material, the liquidcrystals are transparent in the absence of an electric field (e.g., zeroelectric field) but light scattering upon application of an electricfield.

In one example in which the layer of optically active material 22 isimplemented using liquid crystals, the optically active materialincludes liquid crystals and a dichroic dye to provide a guest-hostliquid crystal mode of operation. When so configured, the dichroic dyecan function as a guest compound within the liquid crystal host. Thedichroic dye can be selected so the orientation of the dye moleculesfollows the orientation of the liquid crystal molecules. In someexamples, when an electric field is applied to the optically activematerial, there is little to no absorption in the short axis of the dyemolecule, and when the electric field is removed from the opticallyactive material, the dye molecules absorb in the long axis. As a result,the dichroic dye molecules can absorb light when the optically activematerial is transitioned to a scattering state. When so configured, theoptically active material may absorb light impinging upon the materialto prevent an observer on one side of privacy glazing structure 12 fromclearly observing activity occurring on the opposite side of thestructure.

When optically active material 22 is implemented using liquid crystals,the optically active material may include liquid crystal moleculeswithin a polymer matrix. The polymer matrix may or may not be cured,resulting in a solid or liquid medium of polymer surrounding liquidcrystal molecules. In addition, in some examples, the optically activematerial 22 may contain spacer beads, for example having an averagediameter ranging from 3 micrometers to 40 micrometers, to maintainseparation between second substrate 16 and flexible substrate 24 (e.g.,such as spacer beads 23 illustrated in FIG. 2).

In another example in which the layer of optically active material 22 isimplemented using a liquid crystal material, the liquid crystal materialturns hazy when transitioned to the privacy state. Such a material mayscatter light impinging upon the material to prevent an observer on oneside of privacy glazing structure 12 from clearly observing activityoccurring on the opposite side of the structure. Such a material maysignificantly reduce regular visible transmittance through the material(which may also be referred to as direct visible transmittance) whileonly minimally reducing total visible transmittance when in the privacystate, as compared to when in the light transmitting state. When usingthese materials, the amount of scattered visible light transmittingthrough the material may increase in the privacy state as compared tothe light transmitting state, compensating for the reduced regularvisible transmittance through the material. Regular or direct visibletransmittance may be considered the transmitted visible light that isnot scattered or redirected through optically active material 22.

Another type of material that can be used as the layer of opticallyactive material 22 is a suspended particle material. Suspended particlematerials are typically dark or opaque in a non-activated state butbecome transparent when a voltage is applied. Yet other examples ofmaterials that can be used as optically active material 22 includethermochromic materials that change visible transmittance in response tochanging temperature and photochromic materials that change visibletransmittance in response to changing amounts of light.

Independent of the specific type of material(s) used for the layer ofoptically active material 22, the material can change from a lighttransmissive state in which privacy glazing structure 12 is intended tobe transparent to a privacy state in which visibility through theinsulating glazing unit is intended to be reduced. Optically activematerial 22 may exhibit progressively decreasing direct visibletransmittance when transitioning from a maximum light transmissive stateto a maximum privacy state. Similarly, optically active material 22 mayexhibit progressively increasing direct visible transmittance whentransitioning from a maximum privacy state to a maximum transmissivestate. The speed at which optically active material 22 transitions froma generally transparent transmission state to a generally opaque privacystate may be dictated by a variety factors, including the specific typeof material selected for optically active material 22, the temperatureof the material, the electrical voltage applied to the material, and thelike.

Depending on the type of material used for optically active material 22,the material may exhibit controllable darkening. As noted above,controllable darkening refers to the ability of the optically activematerial to transition between a high visible light transmission state(a bright state), a low visible light transmission dark state, andoptionally intermediate states therebetween, and vice versa, bycontrolling an external energy source applied to the optically activematerial. When optically active material 22 is so configured, thevisible transmittance through the cell formed by flexible material 24,optically active material 22, and second substrate 16 may be greaterthan 40% when optically active material 22 is transitioned to the highvisible transmission state light state, such as greater than 60%. Bycontrast, the visible transmittance through the cell may be less than 5percent when optically active material 22 is transitioned to the lowvisible light transmission dark state, such as less than 1%. Visibletransmittance can be measured according to ASTM D1003-13.

Additionally or alternatively, optically active material 22 may exhibitcontrollable light scattering. As noted above, controllable lightscattering refers to the ability of the optically active material totransition between a low visible haze state, a high visible haze state,and optionally intermediate states therebetween, and vice versa, bycontrolling an external energy source. When optically active material 22is so configured, the transmission haze through the cell formed byflexible material 24, optically active material 22, and second substrate16 may be less than 10% when optically active material 22 istransitioned to the low visible haze state, such as less than 2%. Bycontrast, the transmission haze through the cell may be greater than 85%when optically active material 22 is transitioned to the high visiblehaze state and have a clarity value below 50%, such as a transmissionhaze greater than 95% and a clarity value below 30%. Transmission hazecan be measured according to ASTM D1003-13. Clarity can be measuredusing a BYK Gardener Haze-Gard meter, commercially available fromBYK-GARDNER GMBH.

In the example of FIG. 1, optically active material 22 is positionedbetween second substrate 16 and flexible substrate 24. Flexiblesubstrate 24 can be bonded about its perimeter to second substrate 16(FIGS. 3 and 4) to form a cavity in which optically active material 22is positioned. For example, second substrate 16 may define a firstsurface 26A and the second surface 26B opposite the first surface. Thefirst surface 26A of the second substrate may face between-pane space20, such that the first surface is positioned closer to the between panespace than the second surface. The flexible substrate 24 may also definea first surface 28A and a second surface 28B opposite the first surface.The second surface 28B of the flexible substrate may be exposed to theopen atmosphere of the between-pane space 20, such that the firstsurface 28A is positioned closer to second substrate 16 than the secondsurface 28B. Optically active material 22 can be positioned between thefirst surface 26A of the second substrate 16 and the first surface 28Aof the flexible substrate. In some examples, optically active material22 is positioned in contact with the first surface 26A of the secondsubstrate 16 and the first surface 28A, such that the two surfaces formrespective walls of the cavity containing the optically active material.

First substrate 14 and second substrate 16 may be fabricated from avariety of different materials and, in different examples, may each befabricated from the same material or may be fabricated from differentmaterials. In general, at least second substrate 16 is fabricated frommaterial that has more structural rigidity than the material used tofabricate flexible substrate 24. In some examples, first substrate 14and/or second substrate 16 may be constructed of clear plastic or clearglass. For example, first substrate 14 and/or second substrate 16 may beformed of plastic such as, e.g., a fluorocarbon plastic, polypropylene,polyethylene, polyester, or polycarbonate. In other examples, firstsubstrate 14 and/or second substrate 16 may be formed from multipledifferent types of materials. For example, the substrates may be formedof a laminated glass, which may include two panes of glass bondedtogether with polyvinyl butyral. In yet other examples, the first paneand/or second pane may be constructed of materials that are nottransparent such as translucent materials or even opaque materials,which may or may not block light transmission through the panes.

In one example, second substrate 14 and/or second substrate 16 may beare constructed of glass. In various examples, the glass may be aluminumborosilicate glass, sodium-lime (e.g., sodium-lime-silicate) glass, oranother type of glass. In addition, the glass may be clear or the glassmay be colored, depending on the application. Although the glass can bemanufactured using different techniques, in some examples the glass ismanufactured on a float bath line in which molten glass is deposited ona bath of molten tin to shape and solidify the glass. Such an exampleglass may be referred to as float glass.

When first substrate 14 and/or second substrate are manufactured ofglass, the glass may or may not be thermally strengthened.Thermally-strengthened glass is generally stronger and more shatterresistant than glass that is not thermally-strengthened. Accordingly,incorporating one or more thermally strengthened glass panes in privacyglazing structure 12 can provide additional strength and shatterresistance, e.g., as compared to when the privacy glazing unit isconstructed without using thermally strengthened glass. For example,utilizing thermally strengthened glass for second substrate 16 mayprovide additional strength to breakage of the exposed substrateprotecting optically active material 22.

An example of a thermally-strengthened glass is tempered glass. Temperedglass is generally fabricated by heating the glass until the glassreaches a stress-relief point temperature (which may be referred to asthe annealing temperature) and thereafter rapidly cooling the glass toinduce compressive stresses in the surface of the glass. Tempered glassmay exhibit a surface compression of greater than 10,000 pounds persquare inch (psi), as determined in accordance with ASTM C1048-04.Another example of a thermally-strengthened glass is Heat Strengthenedglass, which may exhibit a strength between tempered glass and annealedglass. Annealed glass is generally fabricated by heating the glass untilthe glass reaches a stress-relief point temperature (which may also bereferred to as the annealing temperature) and thereafter slowly coolingthe glass to relieve internal stresses. In some examples, HeatStrengthened glass exhibits a surface compression of approximately 5,000psi, as determined in accordance with ASTM C1048-04.

Independent of the specific type of material used to first substrate 14and/or second substrate 16, the surfaces of the substrates may not beperfectly planar. Rather, in practice, there may be depth variationsacross the surfaces of the substrates that cause surface waviness orother surface non-planarity. For example, with respect to secondsubstrate 16, the first surface 26A may not reside entirely within asingle plane (e.g., Z-Y plane indicated on FIG. 1) but may insteadcontain regions that project toward between-pane space 20 (e.g., in thenegative X-direction indicated on FIG. 1) relative to other regionsand/or regions that are recessed away from between-pane space 20 (e.g.,in the positive X-direction indicated on FIG. 1) relative to otherregions. As a result, the first surface 26A of second substrate 16 maynot reside in a single plane but may instead have continuous (e.g.,repeating) or discontinuous regions that are out of plane with respectto a midline of the first surface.

FIG. 2 is a sectional illustration of privacy glazing structure 12 takenalong the A-A sectional line illustrated on FIG. 1 showing an examplesurface non-planarity that second substrate 16 may exhibit. As shown inthis example, first surface 26A of second substrate 16 does not resideentirely within a single plane (e.g., Z-Y plane indicated on FIG. 1) butinstead projects into between-pane space 20 and/or is recessed away frombetween-pane space relative to other sections of the surface. Inparticular, in the illustrated example, first surface 26A is illustratedas having a waveform pattern that includes peaks 30 and valleys 32relative to a midline 34 of the first surface 26A. Each peak 30 isseparated from an adjacent peak by a valley. Such a waveform defect mayoccur during the fabrication of second substrate 16 as the substrate isheated and passed over transport rollers, e.g., causing regions betweenadjacent transport rollers to sag and create a waveform defect. AlthoughFIG. 2 illustrates one example configuration of a non-planar surfacethat second substrate 16 may exhibit, it should be appreciated that thedisclosure is not limited in this respect.

For example, second substrate 16 may exhibit an edge kink non-planarityin addition to or in lieu of a roller wave non-planarity. Edge kink maybe characterized by an upward or downward bow or curl at the leadingedge and/or trailing edge of the substrate. Edge kink may be caused bythe leading and trailing edges of the substrate being unsupported asthey leave one roll and travel to an adjacent roll during the temperingprocessing, e.g., as the unsupported weight causes the edge to benddown.

In some examples, second substrate 16 has a non-planar first surface 26Acharacterized by an optical roll wave distortion value. The optical rollwave distortion value can be measured according to ASTM-C-1651. Ingeneral, optical roll wave distortion is measured according to theformula:D=(4π² W/L ²)/1000.

In the equation above, D is in millidiopters, W is the roll wave depth(or peak-to-valley depth), and L is the peak-to-peak or valley-to-valleywavelength of the roll wave. The distortion D may be measured in themiddle of second substrate 16 as well as along the edges of thesubstrate. For example, the distortion of the second substrate 16 may bemeasured for the centermost 90% area of first surface 26A of secondsubstrate 16 and/or the peripheral-most 90% area of first surface 26A ofsecond substrate 16.

In some examples, second substrate 16 exhibits an optical roll wavedistortion value of at least 10 millidiopters, such as at least 20millidiopters, at least 50 millidiopters, or at least 75 millidiopters.For example, when measuring the centermost 90% area of first surface 26Aof second substrate 16, the first surface may exhibit an optical rollwave distortion ranging from 10 millidiopters to 180 millidiopters, suchas from 50 millidiopters to 150 millidiopters. When measuring theperipheral-most 90% area of first surface 26A of second substrate 16,the first surface may exhibit an optical roll wave distortion rangingfrom 25 millidiopters to 400 millidiopters, such as from 100millidiopters to 350 millidiopters. It should be appreciated that theforegoing values are examples and a non-planar substrate according tothe disclosure may exhibit different optical roll wave distortionvalues.

In general, second substrate 16 is a comparatively rigid substrate suchthat shape and/or structure of first surface 26A (e.g., shape and/orstructure of the non-planar regions) does not change during the servicelife of the substrate. In some examples, second substrate 16 has athickness (e.g., in the X-direction indicated on FIG. 2) greater than1.2 mm, such as a thickness ranging from 2.0 mm to 4.8 mm. In oneexample, second substrate 16 has a thickness of 2.2 mm. First substrate14 (FIG. 1) may have the same thickness as second substrate 16 or mayhave a different thickness. In either case, the rigidity of secondsubstrate 16 may be characterized by its Young's modulus, which measuresthe stiffness of the material. In some examples, second substrate 16exhibits a Young's modulus ranging from 50 GPa to 100 GPa at roomtemperature, such as from 65 GPa to 85 GPa.

To accommodate the non-planarity of first surface 26A of secondsubstrate 16, some examples of the present disclosure utilize flexiblesubstrate 24 to sandwich optically active material 22 to the firstsurface of the second substrate. Flexible substrate 24 may besufficiently flexible to conform to the non-planarity of first surfaceof the second substrate. For example, flexible substrate 24 may mirroror adopt the surface profile of first surface 26A, e.g., such that firstsurface 28A and/or second surface 28B of the flexible substrate mirrorthe shape profile of first surface 26A of second substrate 16. When soconfigured, flexible substrate 24 may have peaks 34 that overlay and arealigned with peaks 30 (e.g., in the X-direction indicated on FIG. 2) andvalleys 36 that overlay and are aligned with valleys 32.

To configure flexible substrate 24 to be sufficiently flexible toconform to surface contours of first surface 26A of second substrate 16,the flexible substrate may be formed of a material and/or have athickness effective to follow the contour of an underlying layer (e.g.,second substrate 16 to which the flexible substrate is bonded. Indifferent examples, flexible substrate 24 may be fabricated from glassor a polymeric material. When flexible substrate 24 is formed of glass,the glass may be an aluminosilicate glass or a borosilicate glass, suchas Willow® glass sold by Corning®. When flexible substrate 24 is formedof a polymer, the substrate may be formed as a single layer of polymericmaterial or multiple layers of polymeric material joined together. Ingeneral, the polymeric material may be selected to be chemicallycompatible with optically active material 22 and provide suitablevisible transmittance characteristics for the privacy glazing structure.As examples, flexible substrate 24 may be formed of PET (polyethyleneterephthalate), PEN (polyethylene naphthalate), PE (polyethylene), PP(polypropylene), PC (polycarbonate), or TAC (cellulose triacetate).

In some examples, flexible substrate 24 is constructed of a materialthat provides a coefficient of thermal expansion consistent with thecoefficient of thermal expansion of the material used to fabricatesecond substrate 16. If flexible substrate 24 is constructed of materialthat has too great of a thermal expansion mismatch with that of secondsubstrate 16, the flexible substrate may have a tendency to detach fromthe second substrate during thermal cycling. This is because theinconsistent thermal expansion of the two substrates may create stressesand/or shear forces between the substrates, which may overcome the forceof the adhesive holding the flexible substrate to the second substrate.By configuring flexible substrate 24 and second substrate 16 to havesufficiently matched coefficients of thermal expansion, the twosubstrates may expand and contract sufficiently equivalent amountsduring thermal cycling to prevent detachment of the substrates from eachother.

In some examples, flexible substrate 24 has a coefficient of thermalexpansion that falls within a range from 20% of the coefficient ofthermal expansion of the second substrate 16 to 120% of the coefficientof thermal expansion of the second substrate, such as from 20% of thecoefficient of thermal expansion of the second substrate to 100% of thecoefficient of thermal expansion of the second substrate. For example,flexible substrate 24 may have a coefficient of thermal expansionranging from 5 ppm/° F. to 110 ppm/° F., such as from 7 ppm/° F. to 50ppm/° F., or from 10 ppm/° F. to 45 ppm/° F. In these examples, secondsubstrate 16 may have a coefficient of thermal expansion ranging from 5ppm/° F. to 35 ppm/° F., such as from 7.5 ppm/° F. to 25 ppm/° F.

In applications where flexible substrate 24 is located inside ofbetween-pane space 20 (FIG. 1), the flexible substrate may be shieldedfrom adverse environmental conditions by first substrate 14, secondsubstrate 16, and spacer 18. Accordingly, while flexible substrate 24may provide environmental barrier properties to optically activematerial 22, the flexible substrate need not provide these performancecharacteristics in certain applications. Rather, in some suchapplications, flexible substrate 24 may be configured for flexibilityrather than environmental barrier properties, which may cause acorresponding loss and flexibility. In some examples, flexible substratehas a water vapor transmission rate greater than 10 g/m²-24 hours, suchas a water vapor transmission rate ranging from 10 g/m²-24 hours to 40g/m²-24 hours.

Independent of the specific material(s) used to fabricate flexiblesubstrate 24, the substrate may be thinner than second substrate 16.This can allow the flexible substrate to conform to the surfacevariations of second substrate 16. As examples, flexible substrate 24may have a thickness (e.g., in the X-direction indicated on FIG. 2) lessthan 1 mm, such as less than 0.5 mm, or less than 0.25 mm. For example,flexible substrate 24 may have a thickness ranging from 0.0125 mm to0.25 mm, such as from 0.025 mm to 0.05 mm.

The flexibility of flexible substrate 24 may be characterized by itsYoung's modulus. In general, the lower the Young's modulus value forflexible substrate 24, the more flexible the substrate. Depending on thetype of material used to fabricate flexible substrate 24, the substratemay exhibit a Young's modulus less than 10 GPa, such as less than 5 GPa.For example, flexible substrate 24 may exhibit a Young's modulus rangingfrom 1.5 GPa to 5 GPa (e.g., when the substrate is fabricated from PETor a similar polymeric material). Accordingly, a flexible substrate 24may exhibit a Young's modulus ranging from 1% to 10% of the Young'smodulus of second substrate 16, such as from 1% to 7% of the Young'smodulus of second substrate 16.

Flexible substrate 24 may also be characterized by its flexuralrigidity. In general, flexural rigidity is a measure of stiffness and isthe product of the modulus of elasticity and moment of inertia dividedby the length of the member. When flexible substrate 24 has acomparatively high flexural rigidity, it may not be sufficientlyflexible to conform and maintain adherence to second substrate 16.Accordingly, in some configurations, flexible substrate 24 has aflexural rigidity less than 10 Newton-millimeter, such as less than 5N-mm. For example, flexible substrate 24 may have a flexural rigidityranging from 0.001 N-mm to 3.0 N-mm (e.g., when flexible substrate 24 isPET). By contrast, second substrate 16 may have a flexural rigiditygreater than 35 N-mm, such as greater than 45 N-mm.

To help protect optically active material 22 from ultraviolet light thatmay degrade the optically active material over time, flexible substrate24 may be configured as a UV blocking substrate. In some examples,flexible substrate 24 is fabricated from a material containing UVblocking agents. Example UV blocking agents include ultravioletabsorbers such as oxanilides, benzophenones, benzotriazoles, andhydroxyphenyltriazines, as well as hindered amine light stabilizers,such as hindered amine light stabilizers that contain a substituted2,2,6,6-tetramethylpiperidine ring. Additionally or alternatively,flexible substrate 24 may be coated with a UV blocking coating (e.g., onsecond surface 28B) to inhibit ultraviolet radiation from passingthrough the flexible substrate and impinging upon optically activematerial 22. Configuring flexible substrate 24 with the UV blockingproperties can be helpful both to protect the underlying opticallyactive material 22 as well as to prevent degradation of flexiblesubstrate 24 itself. For example, when flexible substrate is formed of apolymeric material, the polymeric material may have a tendency to turn ayellow tint or otherwise degrade if exposed to unblocked ultravioletlight during the course of its service life. Configuring flexiblesubstrate 24 with UV blocking properties, for example either in the formof additives to the flexible substrate and/or in overlaying coating, canreduce or eliminate such degradation of the flexible substrate.

The amount of light blocked by flexible substrate 24 can becharacterized by measuring transmittance through the substrate at awavelength of 380 nm, which may be referred to as a T₃₈₀ value. Flexiblesubstrate 24 may exhibit a T₃₈₀ less than 5%, such as less than 3%, orless than 2%.

As mentioned above, flexible substrate 24 may be sufficiently flexibleto conform to the surface profile and contours of second substrate 16.Flexible substrate 24 may conform to the profile of first surface 26A ofsecond substrate 16 such that the cavity defined between the flexiblesubstrate and the second substrate has a substantially uniform thickness(in the X-direction indicated on FIG. 2) and, correspondingly, opticallyactive material 22 in the cavity likewise has a substantially uniformthickness across the entire surface of privacy glazing structure 12(across the Z-Y plane indicated on FIG. 1). The distance between firstsurface 26A of second substrate 16 and first surface 28A of flexiblesubstrate 24 (which defines the thickness of optically active material22) may vary depending on the type of material selected to be used asthe optically active material. In some examples, such as examples inwhich optically active material 22 includes liquid crystals, thedistance may range from 5 micrometers to 35 micrometers. In otherexamples, such as examples in which the optically active material is anelectrochromic material, the distance may range from 80 microns to 120microns.

The distance between first surface 26A of second substrate 16 and firstsurface 28A of flexible substrate 24 (and correspondingly the thicknessof optically active material 22) may vary by less than 10 percent acrossthe entirety of privacy glazing structure 12, such as less than 5percent, or less than 3 percent. For example, depending on theconfiguration of the glazing assembly, the distance between firstsurface 26A of second substrate 16 and first surface 28A of flexiblesubstrate 24 may vary by less than 5 microns across the entirety ofprivacy glazing structure 12, such as less than 3 microns.

To attach flexible substrate 24 to second substrate 16, the flexiblesubstrate may be bonded about its perimeter to the second substrate.FIG. 3 is a sectional illustration of privacy glazing structure 12 takenalong the B-B sectional line illustrated on FIG. 1 showing an examplebonding arrangement of flexible substrate 24 to second substrate 16. Asshown in this example, flexible substrate 24 is bonded about itsperimeter inside of the between-pane space to the first surface ofsecond substrate 16. Flexible substrate 24 of may be bonded about itsentire perimeter, or boundary defining the extent of the flexiblesubstrate, to second substrate 16 to form an enclosed cavity containingthe optically active material.

The specific technique and materials used to bond flexible substrate 24to second substrate 16 may vary depending on the type of material usedto fabricate the flexible substrate. In some examples, flexiblesubstrate 24 is bonded via ultrasonic welding or melt bonding to thesecond substrate. In other examples, an adhesive is used to bondflexible substrate 24 to second substrate 16. When an adhesive is used,the adhesive may be an acrylate, a methacrylate, a urethane, an epoxy,or yet other suitable type of adhesive.

To prevent detachment of the flexible substrate to the rigid substrateto which it is bonded, the adhesive may have sufficient shear strengthto hold the flexible substrate to the rigid substrate over the servicelife of the privacy glazing structure. In some examples, the adhesiveexhibits a shear strength of at least 50 Newtons/mm², such as at least60 N/mm², or at least 75 N/mm². For example, the adhesive may exhibit ashear strength ranging from 50 N/mm² to 100 N/mm².

In the example of FIG. 3, flexible substrate 24 is bonded to secondsubstrate 16 with an adhesive 40. The adhesive has a width 42 over whichit is in contact with both the flexible substrate and the secondsubstrate. In some examples, the width 42 of adhesive 40 may be greaterthan 0.5 mm, such as greater than 1 mm, or greater than 2 mm. Forexample, the width 42 of adhesive 40 may range from 1 mm to 10 mm.Although the width 42 of adhesive 40 is illustrated as being constantabout the perimeter of flexible substrate 24, in other configurations,the width of the adhesive may vary about the perimeter of the flexiblesubstrate.

In the illustrated configuration, flexible substrate 24 is shown asbeing inwardly offset (within the interior of the between-pane space)from spacer 18. When so configured, flexible substrate 24 is notpositioned between spacer 18 and the portion of second substrate 16 towhich the spacer is bonded. This can be useful to provide a better sealbetween the spacer and the second substrate than if the flexiblesubstrate is interposed between the spacer and the substrate. That beingsaid, in other examples, flexible substrate 24 may extend below the topedge of spacer 18 such that the flexible substrate is positioned betweenat least a portion of the spacer and second substrate 16.

FIG. 4 is a side view illustration of privacy glazing 12 showing anexample arrangement of flexible substrate 24 relative to spacer 18. Inthe illustrated example, spacer 18 is illustrated as a tubular spacerthat is positioned between the first substrate 14 and the secondsubstrate 16. The tubular spacer defines a hollow lumen or tube which,in some examples, is filled with desiccant (not illustrated in FIG. 42).Spacer 18 includes a first side surface 44, a second side surface 46, atop surface 48 connecting first side surface 44 to second side surface46, and a bottom surface 50 also connecting first side surface 44 tosecond side surface 46. First side surface 44 of spacer 18 is positionedadjacent the first substrate 14 while second side surface 46 of thespacer is positioned adjacent the second substrate 16. Top surface 48 isexposed to the between-pane space 20. In some examples, top surface 48of spacer 18 includes openings that allow gas within between-pane space20 to communicate into the lumen of the spacer. When spacer 18 is filledwith desiccating material, gas communication can help remove moisturefrom within the between-pane space, helping to prevent condensationbetween the panes.

In addition, spacer 18 in the example of FIG. 4 includes at least onesealant positioned between spacer 18 and opposing substrates. Inparticular, in the example of FIG. 4, spacer 18 is illustrated asincluding a primary sealant 52 and a secondary sealant 54. Primarysealant 52 is positioned between a portion of the first side surface 44extending substantially parallel to the first substrate 14 and a portionof second side surface 46 extending substantially parallel to the secondsubstrate 16. Secondary sealant 54 is positioned between a portion offirst side surface 44 diverging away from the first substrate 14 and aportion of second side surface 46 diverging away from the secondsubstrate 16.

Spacer 18 can be fabricated from aluminum, stainless steel, athermoplastic, or any other suitable material. Advantageous glazingspacers are available commercially from Allmetal, Inc. of Itasca, Ill.,U.S.A. Example materials that may be used as primary sealant 52 include,but are not limited to, extrudable thermoplastic materials, butyl rubbersealants (e.g., polyisobutylene-based thermoplastics), polysulfidesealants, and polyurethane sealants. In some examples, primary sealant52 is formed from a butyl rubber sealant that includes siliconefunctional groups or a polyurethane sealant that includes siliconefunctional groups. Example materials that may be used as secondarysealant 54 include acrylate polymers, silicone-based polymers,extrudable thermoplastic materials, butyl rubber sealants (e.g.,polyisobutylene-based thermoplastics), polysulfide sealants,polyurethane sealants, and silicone-based sealants. For example,secondary sealant 54 may be formed from a butyl rubber sealant thatincludes silicone functional groups or a polyurethane sealant thatincludes silicone functional groups.

In the illustrated example, the terminal edge of flexible substrate 24is offset from the top surface 48 of spacer 18 a distance 56. Ingeneral, the distance 56 may be minimized to avoid creating a sight lineor visual discontinuity between the spacer and the flexible substrate(as well as the terminal edge of the underlying optically activematerial 22 and the spacer). In some examples, the distance 56 is lessthan 5 millimeters, such as less than 2 millimeters. For example,distance 56 may range from 0.1 millimeters to 5 millimeters.

With further reference to FIG. 1, privacy glazing structure 12 includesbetween-pane space 20. To minimize thermal exchange across structure 12,between-pane space 20 can be filled with an insulative gas or evenevacuated of gas. For example, between-pane space 20 may be filled withan insulative gas such as argon, krypton, or xenon. In suchapplications, the insulative gas may be mixed with dry air to provide adesired ratio of air to insulative gas, such as 10 percent air and 90percent insulative gas. In other examples, between-pane space 20 may beevacuated so that the between-pane space is at vacuum pressure relativeto the pressure of an environment surrounding privacy glazing structure12. In yet other examples, between-pane space 20 is not filled with aninsulative gas or evactuated of gas but may instead be filled with air(e.g., dry air).

Spacer 18 holds first substrate 14 generally parallel to and spacedapart from second substrate 16 to define between-pane space 20. Spacer18 can extend around the entire perimeter of privacy glazing structure12 to hermetically seal the between-pane space 20 from gas exchange witha surrounding environment. In some examples, the distance between firstsubstrate 14 and second substrate 16 maintained by spacer 18 is greaterthan approximately 6 millimeters (mm) such as, e.g., from 6.5 mm to 21mm, or from approximately 8 mm to approximately 10 mm.

Depending on application, first substrate 14, second substrate 16,and/or flexible substrate 24 may be coated with one or more functionalcoatings to modify the performance of privacy glazing structure 12.Example functional coatings include, but are not limited to,low-emissivity coatings, solar control coatings, and photocatalyticcoatings. In general, a low-emissivity coating is a coating that isdesigned to allow near infrared and visible light to pass through a panewhile substantially preventing medium infrared and far infraredradiation from passing through the panes. A low-emissivity coating mayinclude one or more layers of infrared-reflection film interposedbetween two or more layers of transparent dielectric film. Theinfrared-reflection film may include a conductive metal like silver,gold, or copper. Advantageous low-emissivity coatings include theLoE-180™, LoE-272™, and LoE-366™ coatings available commercially fromCardinal CG Company of Spring Green, Wis., U.S.A. A photocatalyticcoating, by contrast, may be a coating that includes a photocatalyst,such as titanium dioxide. In use, the photocatalyst may exhibitphotoactivity that can help self-clean, or provide less maintenance for,the panes. Advantageous photocatalytic coatings include the NEAT®coatings available from Cardinal CG Company.

In general, the surfaces of privacy glazing structure 12 are numberedsequentially starting with a surface of the glass that is facing anexternal (e.g., outside environment). When privacy glazing structure 12in the example of FIG. 1 is positioned so that the first substrate 14faces an exterior environment and the second substrate 16 faces aninterior environment, the surface of the first substrate facing theexterior environment may be designated the #1 surface while the oppositesurface of the substrate facing between-pane space 20 may be designatedthe #2 surface. Continuing with this example, the second surface 28B offlexible substrate 24 may be designated the #3 surface while theopposite first surface 28A of the flexible substrate may be designatedthe #4 surface. Further, the first surface 26A of the second substrate16 may be designated the #5 surface while the opposite second surface26B of the second substrate is the #6 surface.

When a low emissivity coating is used, the low emissivity coating may bepositioned on any surface of any substrate of privacy glazing structure12, including on multiple surfaces of the same or different substratesof the unit. In instances when privacy glazing structure 12 includes asingle low emissivity coating, for example, the coating may bepositioned on the #2 and/or #3 surfaces of unit. When a photocatalyticcoating is used, the photocatalytic coating is typically positioned onthe #1 surface of privacy glazing structure 12. Another example coatingthat may be used on privacy glazing structure 12 is an anti-reflectivecoating. When used, the anti-reflective coating may be positioned on the#1 surface of privacy glazing structure 12 and/or the #2 and/or #5surfaces of the unit.

The substrates of privacy glazing structure 12 can be coated withadditional or different coatings depending on the application. Forexample, when optically active material 22 is selected to be anelectrically controllable optically active material, privacy glazingstructure 12 may include electrodes positioned on opposite sides of thematerial to control the optical state of the material. The electrodescan be physically separate from flexible substrate 24 and secondsubstrate 16 or, instead, can be formed by depositing an electricallyconductive coating on one or both of the substrates. In one example,second substrate 16 and flexible substrate 24 are each coated with atransparent conductive oxide (“TCO”) coating, such as aluminum-dopedzinc oxide and/or tin-doped indium oxide. The first surface 26A ofsecond substrate 16 and the first surface 28A of flexible substrate 24(or, in other examples, second surface 28B of flexible substrate 24) caneach be coated with a substantially transparent conductive layer tocontrol optically active material 22. The transparent conductive oxidecoatings can be electrically connected to a power source throughelectrical conductors extending through spacer 18. In some examples, thetransparent conductive coating forms wall surfaces of the cavity betweensecond substrate 16 and flexible substrate 24 which optically activematerial 22 contacts. In other examples, one or more other coatings mayoverlay the transparent conductive coating, such as a dielectric overcoat.

When second substrate 16 and/or flexible substrate 24 carry a coatingfacing optically active material 22 (on first surface 26A and/or firstsurface 28A, respectively), the coating may be absent over the region ofthe substrates where adhesive 40 is positioned (FIGS. 3 and 4). Thecoating may be selectively deposited to so as to not be present in theregion where adhesive 40 is to be positioned or may be removed afterdeposition in the region where adhesive 40 is to be positioned.Alternatively, the conductive coating on second substrate 16 may bescribed around the interior perimeter of adhesive 40 to electricallyisolate the adhesive. In either case, in some examples, first surface26A of second substrate 16 and/or first surface 28A of flexiblesubstrate 24 where adhesive 40 is positioned is devoid of any surfacecoatings on the remainder of the substrate(s). As a result, adhesive 40may be in direct contact with first surface 26A of second substrate 16and/or first surface 28A of flexible substrate 24 instead of anintervening coating layer. This may help form a stronger bond betweensecond substrate 16 and flexible substrate 24 than if the flexiblesubstrate is bonded to second substrate 16 through an adhesive bonded toone or more intermediate coating layers.

While privacy glazing structure 12 in the example of FIG. 1 isillustrated as being formed of two comparatively rigid panes—firstsubstrate 14 and second substrate 16—held together via spacer 18, itshould be appreciated that a privacy glazing structure in accordancewith the disclosure can have other configurations and the disclosure isnot limited in this respect. As one example, privacy glazing structure12 may include a third rigid substrate attached via a second spacer tofirst substrate 14 or second substrate 16 to form a triple-pane assemblyhaving two between-pane spaces. As another example, privacy glazingstructure 12 may not include first substrate 14 attached to secondsubstrate 16 via spacer 18 but may instead be a single cell whereflexible substrate 24 forms one exterior surface of the cell andsubstrate 16 forms an opposite exterior surface of the cell. As yet afurther example, second substrate 16 may not be a single substrate butmay instead be implemented as laminated substrate having two rigidsubstrates laminated together which, in combination, form secondsubstrate 16.

Independent of the specific number or configuration of substrates inglazing structure 12, a controlled optical transmission structure thatutilizes flexible substrate 24 in lieu of a rigid substrate may weighless than a comparable structure utilizing the rigid substrate. This canbe useful, in some examples, to allow the controllable opticaltransmission structure to be installed using standard/existinginstallation hardware used for non-controllable optical transmissionstructures. Depending on the specific types and thicknesses of materialsused, the controllable optical transmission unit formed by bondingflexible substrate 24 to second substrate 16, with optically activematerial 22 positioned therebetween, may weigh less than 10 kilogramsper square meter, such as less than 8 kilograms per square meter. Forexample, unit may weigh from 5 kilograms per square meter to 10kilograms per square meter, such as from 6.5 kilograms per square meterto 8.5 kilograms per square meter. As one example, when flexiblesubstrate 24 is formed from 25 micron PET and second substrate 16 is 3.1mm tempered glass coated with a transparent conductive oxide coating,the unit may weigh approximately 7.5 kilograms per square meter. Bycontrast, if the unit were made by sandwiching optically active material22 between to laminated glass substrates for safety, the unit may weighmore than 20 kilograms per square meter.

Various examples have been described. These and other examples arewithin the scope of the following claims.

The invention claimed is:
 1. A privacy glazing structure comprising: afirst rigid substrate of transparent material; a second rigid substrateof transparent material that is generally parallel to the first rigidsubstrate, the second rigid substrate having a first surface and asecond surface opposite the first surface; a tubular spacer positionedbetween the first rigid substrate and the second rigid substrate todefine a between-pane space; a flexible substrate having a first surfaceand a second surface opposite the first surface; a first substantiallytransparent conductive layer carried on the first surface of theflexible substrate; a second substantially transparent conductive layercarried on the first surface of the second rigid substrate facing thebetween-pane space; and an electrically controllable optically activematerial, wherein the flexible substrate is bonded about its perimeterto the first surface of the second rigid substrate to form a cavitytherebetween, the electrically controllable optically active material isdisposed within the cavity, and the flexible substrate is sufficientlyflexible to conform to non-planarity of the second rigid substrate. 2.The structure of claim 1, wherein the flexible substrate is a polymericsheet.
 3. The structure of claim 2, wherein the polymeric sheetcomprises one or more layers formed of polyethylene terephthalate. 4.The structure of claim 1, wherein the flexible substrate isaluminosilicate glass or borosilicate glass.
 5. The structure of claim1, wherein the flexible substrate exhibits a flexural rigidity less than5 N-mm.
 6. The structure of claim 1, wherein the flexible substrateexhibits a T³⁸⁰ less than 2 percent.
 7. The structure of claim 1,wherein the second rigid substrate is tempered float glass.
 8. Thestructure of claim 1, wherein the second rigid substrate has a thicknessranging from 2 mm to 4 mm.
 9. The structure of claim 1, wherein theflexible substrate has a coefficient of thermal expansion, the secondrigid substrate has a coefficient of thermal expansion, and thecoefficient of thermal expansion of the flexible substrate ranges from20 percent of the coefficient of thermal expansion of the second rigidsubstrate to 120 percent of the coefficient of thermal expansion of thesecond rigid substrate.
 10. The structure of claim 1, wherein the firstsubstantially transparent conductive layer and the second substantiallytransparent conductive layer form opposite wall surfaces of the cavity.11. The structure of claim 1, further comprising a third rigid substratelaminated to the second surface of the second rigid substrate.
 12. Thestructure of claim 1, wherein the electrically controllable opticallyactive material is a liquid crystal material having a lighttransmittance that varies in response to application of an electricalfield.
 13. The structure of claim 1, wherein the electricallycontrollable optically active material is selected from the groupconsisting of an electrochromic material and a suspended particlematerial.
 14. The structure of claim 1, wherein the second rigidsubstrate has a compressive strength of at least 8,000 pounds per squareinch.